Received October 16, 2024
Accepted September 01, 2025

Objective:The incidence of monozygotic twinning (MZT) is increased after ART procedures. Despite the considerable number of studies, no clear conclusion has been reached on the possible aetiology of MZT after fertility treatments. The aim of the present study is to analyze the putative factors affecting the incidence of MZT gestations over the period of 8 years. Methods: This retrospective cohort study analyzed 21 autologous (patient´s own oocytes) and heterologous (donor oocytes were used) ICSI cycles of single or double embryo transfers that resulted in monozygotic gestations between 2015 and 2022 in a single IVF center. The frequency and type of monozygotic gestation were recorded and analyzed in a yearly basis. Results:We observed a strong clustering of MZT gestations in two years (2018 and 2019) of the study period. In addition, two cases of heterologous MZT gestation occurred after egg donation from the same donor in two different oocyte collection cycles. Conclusion:Our observations suggest that not a single factor related to ART procedures is the cause of MZT after fertility treatment. Maternal genetic and epigenetic, as well as uncontrolled environmental factors, may be working synergistically to promote the occurrence of monozygotic twinning.